Protective relays can be found in any environment that uses electricity, from factories to power utilities. Relaying protection applications may include: motors, generators, transformers, station-buses, lines and circuits, system grounds, network systems, pilot wires, pilot channels, transmission lines, pilot relaying, backup, reclosing, synchronizing, load-shedding, frequency and many more.
Typically, relays operate in combination with current and potential transformers, which reduce the high currents and potentials to levels usable by the relays, meters and/or instruments. Relays are electrically connected to the system through a test switch terminal. Each test switch can be associated with one or more relays. It is generally necessary to short circuit the line and load terminals when a relay is removed from its case or when an adjacent test switch is opened. The test switch provides this necessary short circuit or bypass feature. Safety hazards and/or transformer damage could occur if this short circuit/bypass function is not performed.
An exemplary prior art test switch is shown in FIG. 1 and generally indicated by the numeral 10. The wide variety of test switches available allows for many types of applications. As is well known to those of ordinary skill in the art, these applications may include test switches with all potential switches, all current switches or some combination thereof.
Test switch 10 includes on its front face 10 switches 12a to 12j arranged in five (5) sets. In the embodiment shown in FIG. 1 for prior art test switch 10 there are two switches, namely switch 12a and 12b, which are associated with a respective current transformer (not shown). Test switch 10 also includes eight (8) potential switches, namely switches 12c and 12d, 12e and 12f, 12g and 12h, 12i and 12j. 
One example of a pair of switches associated with a current transformer is shown in FIGS. 2a and 2b. The paired switches include a switch, such as switch 12a which has a shorting blade 14 and a switch such as switch 12b which does not have a shorting blade. The switch 12a with the shorting blade provides, when opened, the desired short circuit of the line and load terminals when that switch is opened. The switch 12b provides a current test jack 16.
On the rear face of test switch 10, twenty terminals are provided for connection to the relays. When test switch 10 is mounted in a switchboard panel (not shown) the switches 12a to 12j are accessible from the front of the panel and the terminals on the rear face are only accessible from the rear of the panel.
In-service test plugs, in cooperation with matching test switches are designed to be used while the relay is in-service in order to externally test potential, current, or other possible characteristics of the circuit. Use of the test plug does not effect the operation of the circuit itself or any associated protective equipment acting in conjunction with the circuit.
Prior art in-service type test plugs were restricted in their construction and developed exclusively for use with a specific matching switch configuration. Only a limited number of configurations are possible with the old devices, which rendered them useless in the future should new switches or switches with varying sizes be introduced.
Thus, there is a need in the art for an in-service test plug capable of being easily placed in multiple configurations.